1. Field of the Invention
This invention relates to valves, and more particularly to valve handles used to rotate a valve closure member between open and closed positions.
2. Description of the Prior Art
In valves, such as a rotary or piston-type valves, a shaft is rotated for operating a closure member between open and closed positions. An elongated valve handle is typically disposed about and engaged with the shaft of the valve. The handle applies torque to the shaft to rotate the shaft. Many times these type valves are used on a bottom outlet valve of a tank car. Often liquid material stored in these tank cars solidifies or congeals. This solidified material makes it difficult or impossible to rotate the shaft to open the valve. To properly remove the solidified material from the tank car without damaging the valve the material should first be reliquified by heating or other means. This reliquifying, however, takes time. Workers, who are under time pressure to unload the tank cars, do not always attempt to liquify the tank car contents or do not wait the requisite amount of time until the contents are completely liquified. Subsequently, the workers need to forcibly rotate the handle attached to the valve to open the valve. This often results in excessive torque being applied to the shaft which often damages the valve.
It is known in such valves to employ a frangible element adapted to fail and prevent excessive torque from being transmitted to the valve mechanism. These frangible elements typically do not form a portion of the valve handle itself, but are usually integral with a member connected to the shaft of a valve and are not therefore separate, individual pieces. Since these elements are often connected to such a member, the entire member, rather than simply the frangible element, must be replaced when the element fails which adds to the cost of repair. Also, since these members are not typically disposed on an external, readily accessible area, once the frangible elements fail, a great time and effort is required to disassemble the valve assembly to remove and replace the members with the failed elements. Additionally, most valve assemblies with frangible elements have no means of confining the frangible elements once they have failed. These non-confined elements can strike or injure a user or travel elsewhere.